Processes for making ethanol from acetic acid

ABSTRACT

A process for selective formation of ethanol from acetic acid by hydrogenating acetic acid in the presence of first metal, a silicaceous support, and at least one support modifier. Preferably, the first metal is selected from the group consisting of copper, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium, rhenium, molybdenum, and tungsten. In addition the catalyst may comprise a second metal preferably selected from the group consisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium, rhenium, gold, and nickel.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. application Ser. No. 12/588,727,filed Oct. 26, 2009, entitled “Tunable Catalyst Gas Phase Hydrogenationof Carboxylic Acids,” and of U.S. application Ser. No. 12/221,141, filedJul. 31, 2008, entitled “Direct and Selective Production of Ethanol fromAcetic Acid Utilizing a Platinum/Tin Catalyst,” the entireties of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for hydrogenatingacetic acid to form ethanol and to novel catalysts for use in suchprocesses, the catalysts having high selectivities for ethanol.

BACKGROUND OF THE INVENTION

There is a long felt need for an economically viable process to convertacetic acid to ethanol which may be used in its own right orsubsequently converted to ethylene which is an important commodityfeedstock as it can be converted to vinyl acetate and/or ethyl acetateor any of a wide variety of other chemical products. For example,ethylene can also be converted to numerous polymer and monomer products.Fluctuating natural gas and crude oil prices contribute to fluctuationsin the cost of conventionally produced, petroleum or natural gas-sourcedethylene, making the need for alternative sources of ethylene all thegreater when oil prices rise.

Catalytic processes for reducing alkanoic acids and other carbonyl groupcontaining compounds have been widely studied, and a variety ofcombinations of catalysts, supports and operating conditions have beenmentioned in the literature. The reduction of various carboxylic acidsover metal oxides is reviewed by T. Yokoyama et al. in “Fine chemicalsthrough heterogeneous catalysis. Carboxylic acids and derivatives.”Chapter 8.3.1, summarizes some of the developmental efforts forhydrogenation catalysts for various carboxylic acids. (Yokoyama, T.;Setoyama, T. “Carboxylic acids and derivatives.” in: “Fine chemicalsthrough heterogeneous catalysis.” 2001, 370-379.)

A series of studies by M. A. Vannice et al. concern the conversion ofacetic acid over a variety of heterogeneous catalysts (Rachmady W.;Vannice, M. A.; J. Catal. (2002) Vol. 207, pg. 317-330.) The vapor-phasereduction of acetic acid by H₂ over both supported and unsupported ironwas reported in a separate study. (Rachmady, W.; Vannice, M. A. J.Catal. (2002) Vol. 208, pg. 158-169.) Further information on catalystsurface species and organic intermediates is set forth in Rachmady, W.;Vannice, M. A., J. Catal. (2002) Vol. 208, pg. 170-179). Vapor-phaseacetic acid hydrogenation was studied further over a family of supportedPt—Fe catalysts in Rachmady, W.; Vannice, M. A. J. Catal. (2002) Vol.209, pg. 87-98) and Rachmady, W.; Vannice, M. A. J. Catal. (2000) Vol.192, pg. 322-334).

Various related publications concerning the selective hydrogenation ofunsaturated aldehydes may be found in (Djerboua, F.; Benachour, D.;Touroude, R. Applied Catalysis A: General 2005, 282, 123-133; Liberkova,K.; Tourounde, R. J. Mol. Catal. 2002, 180, 221-230; Rodrigues, E. L.;Bueno, J. M. C. Applied Catalysis A: General 2004, 257, 210-211; Ammari,F.; Lamotte, J.; Touroude, R. J. Catal. 2004, 221, 32-42; Ammari, F.;Milone, C.; Touroude, R. J. Catal. 2005, 235, 1-9; Consonni, M.; Jokic,D.; Murzin, D. Y.; Touroude, R. J. Catal. 1999, 188, 165-175; Nitta, Y.;Ueno, K.; Imanaka, T.; Applied Catal. 1989, 56, 9-22.)

Studies reporting activity and selectivity over cobalt, platinum andtin-containing catalysts in the selective hydrogenation ofcrotonaldehyde to the unsaturated alcohol are found in R. Touroude etal. (Djerboua, F.; Benachour, D.; Touroude, R. Applied Catalysis A:General 2005, 282, 123-133 as well as Liberkova, K.; Tourounde, R.; J.Mol. Catal. 2002, 180, 221-230) as well as K. Lazar et al. (Lazar, K.;Rhodes, W. D.; Borbath, I.; Hegedues, M.; Margitfalvi, I. L. HyperfineInteractions 2002, 1391140, 87-96.)

M. Santiago et al. (Santiago, M. A. N.; Sanchez-Castillo, M. A.;Cortright, R. D.; Dumesic, I. A. J. Catal. 2000, 193, 16-28.) discussmicrocalorimetric, infrared spectroscopic, and reaction kineticsmeasurements combined with quantum-chemical calculations.

Catalytic activity in for the acetic acid hydrogenation has also beenreported for heterogeneous systems with rhenium and ruthenium.(Ryashentseva, M. A.; Minachev, K. M.; Buiychev, B. M.; Ishchenko, V. M.Bull. Acad Sci. USSR1988, 2436-2439).

U.S. Pat. No. 5,149,680 to Kitson et al. describes a process for thecatalytic hydrogenation of carboxylic acids and their anhydrides toalcohols and/or esters utilizing platinum group metal alloy catalysts.U.S. Pat. No. 4,777,303 to Kitson et al. describes a process for theproductions of alcohols by the hydrogenation of carboxylic acids. U.S.Pat. No. 4,804,791 to Kitson et al. describes another process for theproduction of alcohols by the hydrogenation of carboxylic acids. Seealso U.S. Pat. Nos. 5,061,671; 4,990,655; 4,985,572; and 4,826,795.

Malinowski et al. (Bull. Soc. Chim. Belg. (1985), 94(2), 93-5), discussreaction catalysis of acetic acid on low-valent titanium heterogenizedon support materials such as silica (SiO₂) or titania (TiO₂).

Bimetallic ruthenium-tin/silica catalysts have been prepared by reactionof tetrabutyl tin with ruthenium dioxide supported on silica. (Loessardet al., Studies in Surface Science and Catalysis (1989), Volume Date1988, 48 (Struct. React. Surf.), 591-600.)

The catalytic reduction of acetic acid has also been studied in, forinstance, Hindermann et al., (Hindermann et al., J. Chem. Res., Synopses(1980), (11), 373), disclosing catalytic reduction of acetic acid oniron and on alkali-promoted iron.

Existing processes suffer from a variety of issues impeding commercialviability including: (i) catalysts without requisite selectivity toethanol; (ii) catalysts which are possibly prohibitively expensiveand/or nonselective for the formation of ethanol and that produceundesirable by-products; (iii) operating temperatures and pressureswhich are excessive; and/or (iv) insufficient catalyst life.

SUMMARY OF THE INVENTION

The present invention relates to processes for hydrogenating acetic acidto make ethanol at high selectivities. In a first embodiment, theinvention is directed to a process for producing ethanol, comprisinghydrogenating acetic acid in the presence of a catalyst comprising afirst metal, a silicaceous support, and at least one support modifier.The first metal may be selected from the group consisting of Group IB,IIB, IIIB, IVB, VB, VIB, VIIB, or VIII transitional metal, a lanthanidemetal, an actinide metal or a metal from any of Groups IIIA, IVA, VA, orVIA. More preferably the first metal may be selected from the groupconsisting of copper, iron, cobalt, nickel, ruthenium, rhodium,palladium, osmium, iridium, platinum, titanium, zinc, chromium, rhenium,molybdenum, and tungsten. The first metal may be present in an amount offrom 0.1 to 25 wt. %, based on the total weight of the catalyst.

In another aspect, the catalyst may comprise a second metal (preferablydifferent from the first metal), which may be selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. In this aspect, the first metal may bepresent, for example, in an amount of from 0.1 to 10 wt. % and thesecond metal may be present in an amount of from 0.1 to 10 wt. %, basedon the total weight of the catalyst. In another aspect, the catalyst maycomprise a third metal (preferably different from the first metal andthe second metal), which may be selected from the group consisting ofcobalt, palladium, ruthenium, copper, zinc, platinum, tin, and rheniumand/or which may be present in an amount of 0.05 and 4 wt. %, based onthe total weight of the catalyst.

Preferably, the first metal is platinum and the second metal is tinhaving a molar ratio of platinum to tin being from 0.4:0.6 to 0.6:0.4.In another preferred combination, the first metal is palladium and thesecond metal is rhenium having molar ratio of rhenium to palladium beingfrom 0.7:0.3 to 0.85:0.15.

In a preferred aspect of the process, at least 10% of the acetic acid isconverted during hydrogenation. Optionally, the catalysts have aselectivity to ethanol of at least 80% and/or a selectivity to methane,ethane, and carbon dioxide of less than 4%. In one embodiment, thecatalyst has a productivity that decreases less than 6% per 100 hours ofcatalyst usage.

The silicaceous support may optionally be selected from the groupconsisting of silica, silica/alumina, calcium metasilicate, pyrogenicsilica, high purity silica, and mixtures thereof and may be present inan amount of 25 wt. % to 99 wt. %, based on the total weight of thecatalyst. Preferably, the silicaceous support has a surface area of from50 m²/g to 600 m²/g.

The support modifier, e.g., metasilicate support modifier, may beselected from the group consisting of (i) alkaline earth metal oxides,(ii) alkali metal oxides, (iii) alkaline earth metal metasilicates, (iv)alkali metal metasilicates, (v) Group IIB metal oxides, (vi) Group IIBmetal metasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIBmetal metasilicates, and mixtures thereof. As one option, the supportmodifier may be selected from the group consisting of oxides andmetasilicates of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, preferably being CaSiO₃. The support modifier may bepresent in an amount of 0.1 wt. % to 50 wt. %, based on the total weightof the catalyst.

In one embodiment, the hydrogenation is performed in a vapor phase at atemperature of from 125° C. to 350° C., a pressure of 10 KPa to 3000KPa, and a hydrogen to acetic acid mole ratio of greater than 4:1.

In another embodiment, the invention relates to a crude ethanol product(optionally obtained from the hydrogenation of acetic acid, as discussedabove), which comprises (a) ethanol in an amount from 15 to 70 wt. %,preferably from 20 to 50 wt. % or, more preferably, from 25 to 50 wt. %;(b) acetic acid in an amount from 0 to 80 wt. %, preferably from 20 to70 wt. % or, more preferably from 44 to 65 wt. %; (c) water in an amountfrom 5 to 30 wt. %, preferably from 10 to 30 wt. % or, more preferably,from 10 to 26 wt; and (d) any other compounds in an amount less than 10wt. %, wherein all weight percents are based on the total weight of thecrude ethanol product. A preferred crude ethanol product comprises theethanol in an amount from 20 to 50 wt. %; the acetic acid in an amountfrom 28 to 70 wt. %; the water in an amount from 10 to 30 wt. %; and anyother compounds in an amount less than 6 wt. %. An additional preferredcrude ethanol product comprises the ethanol in an amount from 25 to 50wt. %; the acetic acid in an amount from 44 to 65 wt. %; the water in anamount from 10 to 26 wt. %; and any other compounds in an amount lessthan 4 wt. %.

In another embodiment, the invention relates to a process for producingethanol comprising hydrogenating acetic acid in the presence of acatalyst comprising:Pt_(v)Pd_(w)Re_(x)Sn_(y)Ca_(p)Si_(q)O_(r),wherein: (i) the ratio of v:y is between 3:2 and 2:3, and/or (ii) theratio of w:x is between 1:3 and 1:5; and p and q are selected such thatp:q is from 1:20 to 1:200 with r being selected to satisfy valencerequirements and v and w being selected such that:

$0.005 \leq \frac{\left( {{3.25\; v} + {1.75\; w}} \right)}{q} \leq {0.05.}$

In yet another embodiment, the invention relates to a process forproducing ethanol comprising hydrogenating acetic acid in the presenceof a catalyst comprising:Pt_(v)Pd_(w)Re_(x)Sn_(y)Al_(z)Ca_(p)Si_(q)O_(r),wherein: (i) v and y are between 3:2 and 2:3, and/or (ii) w and x arebetween 1:3 and 1:5; and p and z and the relative locations of aluminumand calcium atoms present are controlled such that Brønsted acid sitespresent upon the surface thereof are balanced by a support modifier; andp and q are selected such that p:q is from 1:20 to 1:200 with r beingselected to satisfy valence requirements, and v and w are selected suchthat:

$0.005 \leq \frac{\left( {{3.25\; v} + {1.75\; w}} \right)}{q} \leq {0.05.}$

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1A is a graph of the selectivity to ethanol and ethyl acetate usinga SiO₂—Pt_(m)Sn_(1-m) catalyst;

FIG. 1B is a graph of the productivity to ethanol and ethyl acetate ofthe catalyst of FIG. 1A;

FIG. 1C is a graph of the conversion of the acetic acid of the catalystof FIG. 1A;

FIG. 2A is a graph of the selectivity to ethanol and ethyl acetate usinga SiO₂—Re_(n)Pd_(1-n) catalyst;

FIG. 2B is a graph of the productivity to ethanol and ethyl acetate ofthe catalyst of FIG. 2A;

FIG. 2C is a graph of the conversion of the acetic acid of the catalystof FIG. 2A;

FIG. 3A is a graph of the productivity of a catalyst to ethanol at 15hours of testing;

FIG. 3B is a graph of the selectivity of the catalyst of FIG. 3A toethanol;

FIG. 4A is a graph of the productivity of a catalyst to ethanol over 100hours of testing according to another embodiment of the invention;

FIG. 4B is a graph of the selectivity of the catalyst of FIG. 4A toethanol;

FIG. 5A is a graph of productivity of a catalyst to ethanol over 20hours of testing according to another embodiment of the invention;

FIG. 5B is a graph of the selectivity of the catalyst of FIG. 5A toethanol;

FIG. 6A is a graph of the conversion of the catalysts of Example 18;

FIG. 6B is a graph of the productivity of the catalysts of Example 18;

FIG. 6C is a graph of the selectivity at 250° C. of the catalysts ofExample 18; and

FIG. 6D is a graph of the selectivity at 275° C. of the catalysts ofExample 18.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for producing ethanol byhydrogenating acetic acid in the presence of a catalyst. The catalystemployed in the process comprises at least one metal, a silicaceoussupport, and at least one support modifier. The present invention alsorelates to the catalysts used in this process and processes for makingthe catalysts. The hydrogenation reaction may be represented as follows:

It has surprisingly and unexpectedly been discovered that the catalystsof the present invention provide high selectivities to ethoxylates, suchas ethanol and ethyl acetate, and in particular to ethanol, whenemployed in the hydrogenation of acetic acid. Embodiments of the presentinvention beneficially may be used in industrial applications to produceethanol on an economically feasible scale.

The catalyst of the invention comprises a first metal and optionally oneor more of a second metal, a third metal or additional metals on thesupport. In this context, the numerical terms “first,” “second,”“third,” etc., when used to modify the word “metal,” are meant toindicate that the respective metals are different from one another. Thetotal weight of all supported metals present in the catalyst preferablyis from 0.1 to 25 wt. %, e.g., from 0.1 to 15 wt. %, or from 0.1 wt. %to 10 wt. %. For purposes of the present specification, unless otherwiseindicated, weight percent is based on the total weight the catalystincluding metal and support. The metal(s) in the catalyst may be presentin the form of one or more metal oxides. For purposes of determining theweight percent of the metal(s) in the catalyst, the weight of any oxygenthat is bound to the metal is ignored.

The first metal may be a Group IB, IIB, IIIB, IVB, VB, VIB, VIIB, orVIII transitional metal, a lanthanide metal, an actinide metal or ametal from any of Groups IIIA, IVA, VA, or VIA. In a preferredembodiment, the first metal is selected the group consisting of copper,iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium,platinum, titanium, zinc, chromium, rhenium, molybdenum, and tungsten.Preferably, the first metal is selected from the group consisting ofplatinum, palladium, cobalt, nickel, and ruthenium. More preferably, thefirst metal is selected from platinum and palladium. When the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the availability of platinum.

As indicated above, the catalyst optionally further comprises a secondmetal, which typically would function as a promoter. If present, thesecond metal preferably is selected from the group consisting of copper,molybdenum, tin, chromium, iron, cobalt, vanadium, tungsten, palladium,platinum, lanthanum, cerium, manganese, ruthenium, rhenium, gold, andnickel. More preferably, the second metal is selected from the groupconsisting of copper, tin, cobalt, rhenium, and nickel. More preferably,the second metal is selected from tin and rhenium.

Where the catalyst includes two or more metals, one metal may act as apromoter metal and the other metal is the main metal. For instance, witha platinum/tin catalyst, platinum may be considered to be the main metaland tin may be considered the promoter metal. For convenience, thepresent specification refers to the first metal as the primary catalystand the second metal (and optional metals) as the promoter(s). Thisshould not be taken as an indication of the underlying mechanism of thecatalytic activity.

If the catalyst includes two or more metals, e.g., a first metal and asecond metal, the first metal optionally is present in the catalyst inan amount from 0.1 to 10 wt. %, e.g. from 0.1 to 5 wt. %, or from 0.1 to3 wt. %. The second metal preferably is present in an amount from 0.1and 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %. Forcatalysts comprising two or more metals, the two or more metals may bealloyed with one another or may comprise a non-alloyed metal solution ormixture.

The preferred metal ratios may vary somewhat depending on the metalsused in the catalyst. In some embodiments, the mole ratio of the firstmetal to the second metal preferably is from 10:1 to 1:10, e.g., from4:1 to 1:4, from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.It has now surprisingly and unexpectedly been discovered that forplatinum/tin catalysts, platinum to tin molar ratios on the order offrom 0.4:0.6 to 0.6:0.4 (or about 1:1) are particularly preferred inorder to form ethanol from acetic acid at high selectivity, conversionand productivity, as shown in FIGS. 1A, 1B and 1C. Selectivity toethanol may be further improved by incorporating modified supports asdescribed throughout the present specification.

Molar ratios other than 1:1 may be preferred for other catalysts. Withrhenium/palladium catalysts, for example, higher ethanol selectivitiesmay be achieved at higher rhenium loadings than palladium loadings. Asshown in FIGS. 2A, 2B and 2C, preferred rhenium to palladium molarratios for forming ethanol in terms of selectivity, conversion andproduction are on the order of 0.7:0.3 to 0.85:0.15, or about 0.75:0.25(3:1). Again, selectivity to ethanol may be further improved byincorporating modified supports as described throughout the presentspecification.

In embodiments when the catalyst comprises a third metal, the thirdmetal may be selected from any of the metals listed above in connectionwith the first or second metal, so long as the third metal is differentfrom the first and second metals. In preferred aspects, the third metalis selected from the group consisting of cobalt, palladium, ruthenium,copper, zinc, platinum, tin, and rhenium. More preferably, the thirdmetal is selected from cobalt, palladium, and ruthenium. When present,the total weight of the third metal preferably is from 0.05 and 4 wt. %,e.g., from 0.1 to 3 wt. %, or from 0.1 to 2 wt. %.

In one embodiment, the catalyst comprises a first metal and noadditional metals (no second metal, etc.). In this embodiment, the firstmetal preferably is present in an amount from 0.1 to 10 wt. %. Inanother embodiment, the catalyst comprises a combination of two or moremetals on a support. Specific preferred metal compositions for variouscatalysts of this embodiment of the invention are provided below inTable 1. Where the catalyst comprises a first metal and a second metal,the first metal preferably is present in an amount from 0.1 to 5 wt. %and the second metal preferably is present in an amount from 0.1 to 5wt. %. Where the catalyst comprises a first metal, a second metal and athird metal, the first metal preferably is present in an amount from 0.1to 5 wt. %, the second metal preferably is present in an amount from 0.1to 5 wt. %, and the third metal preferably is present in an amount from0.1 to 2 wt. %. In one exemplary embodiment, the first metal is platinumand is present in an amount from 0.1 to 5 wt. %, the second metal ispresent in an amount from 0.1 to 5 wt. %, and the third metal, ifpresent, preferably is present in an amount from 0.05 to 2 wt. %.

TABLE 1 EXEMPLARY METAL COMBINATIONS FOR CATALYSTS First Metal SecondMetal Third Metal Cu Ag Cu Cr Cu V Cu W Cu Zn Ni Au Ni Re Ni V Ni W PdCo Pd Cr Pd Cu Pd Fe Pd La Pd Mo Pd Ni Pd Re Pd Sn Pd V Pd W Pt Co Pt CrPt Cu Pt Fe Pt Mo Pt Sn Pt Sn Co Pt Sn Re Pt Sn Ru Pt Sn Pd Rh Cu Rh NiRu Co Ru Cr Ru Cu Ru Fe Ru La Ru Mo Ru Ni Ru Sn

Depending primarily on how the catalyst is manufactured, the metals ofthe catalysts of the present invention may be dispersed throughout thesupport, coated on the outer surface of the support (egg shell) ordecorated on the surface of the support.

In addition to one or more metals, the catalysts of the presentinvention further comprise a modified support, meaning a support thatincludes a support material and a support modifier, which adjusts theacidity of the support material. For example, the acid sites, e.g.Brønsted acid sites, on the support material may be adjusted by thesupport modifier to favor selectivity to ethanol during thehydrogenation of acetic acid. The acidity of the support material may beadjusted by reducing the number or reducing the availability of Brønstedacid sites on the support material. The support material may also beadjusted by having the support modifier change the pKa of the supportmaterial. Unless the context indicates otherwise, the acidity of asurface or the number of acid sites thereupon may be determined by thetechnique described in F. Delannay, Ed., “Characterization ofHeterogeneous Catalysts”; Chapter III: Measurement of Acidity ofSurfaces, p. 370-404; Marcel Dekker, Inc., N.Y. 1984, the entirety ofwhich is incorporated herein by reference. It has now been discoveredthat in addition to the metal precursors and preparation conditionsemployed, metal-support interactions may have a strong impact onselectivity to ethanol. In particular, the use of modified supports thatadjust the acidity of the support to make the support less acidic ormore basic surprisingly and unexpectedly has now been demonstrated tofavor formation of ethanol over other hydrogenation products.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol. Suitable support materials may include, forexample, stable metal oxide-based supports or ceramic-based supports.Preferred supports include silicaceous supports, such as silica,silica/alumina, a Group IIA silicate such as calcium metasilicate,pyrogenic silica, high purity silica and mixtures thereof. Othersupports may be used in some embodiments of the present invention,including without limitation, iron oxide, alumina, titania, zirconia,magnesium oxide, carbon, graphite, high surface area graphitized carbon,activated carbons, and mixtures thereof.

In preferred embodiments, the support comprises a basic support modifierhaving a low volatility or that is non-volatile. Low volatilitymodifiers have a rate of loss that is low enough such that the acidityof the support modifier is not reversed during the life of the catalyst.Such basic modifiers, for example, may be selected from the groupconsisting of: (i) alkaline earth oxides, (ii) alkali metal oxides,(iii) alkaline earth metal metasilicates, (iv) alkali metalmetasilicates, (v) Group IIB metal oxides, (vi) Group IIB metalmetasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIB metalmetasilicates, and mixtures thereof. In addition to oxides andmetasilicates, other types of modifiers including nitrates, nitrites,acetates, and lactates may be used in embodiments of the presentinvention. Preferably, the support modifier is selected from the groupconsisting of oxides and metasilicates of any of sodium, potassium,magnesium, calcium, scandium, yttrium, and zinc, and mixtures of any ofthe foregoing. Preferably, the support modifier is a calcium silicate,more preferably calcium metasilicate (CaSiO₃). If the support modifiercomprises calcium metasilicate, it is preferred that at least a portionof the calcium metasilicate is in crystalline form.

The total weight of the modified support, which includes the supportmaterial and the support modifier, based on the total weight of thecatalyst, preferably is from 75 wt. % to 99.9 wt. %, e.g., from 78 wt. %to 97 wt. %, or from 80 wt. % to 95 wt. %. The support modifierpreferably is provided in an amount sufficient to adjust the acidity,e.g., by reducing the number or reducing the availability of activeBrønsted acid sites, and more preferably to ensure that the surface ofthe support is substantially free of active Brønsted acid sites. Inpreferred embodiments, the support modifier is present in an amount from0.1 wt. % to 50 wt. %, e.g., from 0.2 wt. % to 25 wt. %, from 0.5 wt. %to 15 wt. %, or from 1 wt. % to 8 wt. %, based on the total weight ofthe catalyst. In preferred embodiments, the support material is presentin an amount from 25 wt. % to 99 wt. %, e.g., from 30 wt. % to 97 wt. %or from 35 wt. % to 95 wt. %.

In one embodiment, the support material is a silicaceous supportmaterial selected from the group consisting of silica, silica/alumina, aGroup IIA silicate such as calcium metasilicate, pyrogenic silica, highpurity silica and mixtures thereof. In the case where silica is used asthe silicaceous support, it is beneficial to ensure that the amount ofaluminum, which is a common contaminant for silica, is low, preferablyunder 1 wt. %, e.g., under 0.5 wt. % or under 0.3 wt. %, based on thetotal weight of the modified support. In this regard, pyrogenic silicais preferred as it commonly is available in purities exceeding 99.7 wt.%. High purity silica, as used throughout the application, refers tosilica in which acidic contaminants such as aluminum are present, if atall, at levels of less than 0.3 wt. %, e.g., less than 0.2 wt. % or lessthan 0.1 wt. %. When calcium metasilicate is used as a support modifier,it is not necessary to be quite as strict about the purity of the silicaused as the support material although aluminum remains undesirable andwill not normally be added intentionally. The aluminum content of suchsilica, for example, may be less than 10 wt. %, e.g., less than 5 wt. %or less than 3 wt. %. In cases where the support comprises a supportmodifier in the range of from 2 wt. % to 10 wt. %, larger amount ofacidic impurities, such as aluminum, can be tolerated so long as theyare substantially counter-balanced by an appropriate amount of a supportmodifier.

The surface area of the silicaceous support material, e.g., silica,preferably is at least about 50 m²/g, e.g., at least about 100 m²/g, atleast about 150 m²/g, at least about 200 m²/g or most preferably atleast about 250 m²/g. In terms of ranges, the silicaceous supportmaterial preferably has a surface area of from 50 to 600 m²/g, e.g.,from 100 to 500 m²/g or from 100 to 300 m²/g. High surface area silica,as used throughout the application, refers to silica having a surfacearea of at least about 250 m²/g. For purposes of the presentspecification, surface area refers to BET nitrogen surface area, meaningthe surface area as determined by ASTM D6556-04, the entirety of whichis incorporated herein by reference.

The silicaceous support material also preferably has an average porediameter of from 5 to 100 nm, e.g., from 5 to 30 nm, from 5 to 25 nm orfrom about 5 to 10 nm, as determined by mercury intrusion porosimetry,and an average pore volume of from 0.5 to 2.0 cm³/g, e.g., from 0.7 to1.5 cm³/g or from about 0.8 to 1.3 cm³/g, as determined by mercuryintrusion porosimetry.

The morphology of the support material, and hence of the resultingcatalyst composition, may vary widely. In some exemplary embodiments,the morphology of the support material and/or of the catalystcomposition may be pellets, extrudates, spheres, spray driedmicrospheres, rings, pentarings, trilobes, quadrilobes, multi-lobalshapes, or flakes although cylindrical pellets are preferred.Preferably, the silicaceous support material has a morphology thatallows for a packing density of from 0.1 to 1.0 g/cm³, e.g., from 0.2 to0.9 g/cm³ or from 0.5 to 0.8 g/cm³. In terms of size, the silica supportmaterial preferably has an average particle size, e.g., meaning thediameter for spherical particles or equivalent spherical diameter fornon-spherical particles, of from 0.01 to 1.0 cm, e.g., from 0.1 to 0.5cm or from 0.2 to 0.4 cm. Since the one or more metal(s) that aredisposed on or within the modified support are generally very small insize, they should not substantially impact the size of the overallcatalyst particles. Thus, the above particle sizes generally apply toboth the size of the modified supports as well as to the final catalystparticles.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain NorPro. The Saint-GobainNorPro SS61138 silica contains approximately 95 wt. % high surface areasilica; a surface area of about 250 m²/g; a median pore diameter ofabout 12 nm; an average pore volume of about 1.0 cm³/g as measured bymercury intrusion porosimetry and a packing density of about 0.352 g/cm³(22 lb/ft³).

A preferred silica/alumina support material is KA-160 (Sud Chemie)silica spheres having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, in absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

In embodiments where substantially pure ethanol is to be produced athigh selectivity, as indicated above, controlling the Brønsted acidityof the support material by incorporating a support modifier can be quitebeneficial. One possible byproduct of the hydrogenation of acetic acidis ethyl acetate. According to the present invention, the supportpreferably includes a support modifier that is effective to suppressproduction of ethyl acetate, rendering the catalyst composition highlyselective to ethanol. Thus, the catalyst composition preferably has alow selectivity toward conversion of acetic acid to ethyl acetate andhighly undesirable by-products such as alkanes. The acidity of thesupport preferably is controlled such that less than 4%, preferably lessthan 2% and most preferably less than about 1% of the acetic acid isconverted to methane, ethane and carbon dioxide. In addition, theacidity of the support may be controlled by using a pyrogenic silica orhigh purity silica as discussed above.

In one embodiment, the modified support comprises a support material andcalcium metasilicate as support modifier in an amount effective tobalance Brønsted acid sites resulting, for example, from residualalumina in the silica. Preferably, the calcium metasilicate is presentin an amount from 1 wt. % to 10 wt. %, based on the total weight of thecatalyst, in order to ensure that the support is essentially neutral orbasic in character.

As the support modifier, e.g., calcium metasilicate, may tend to have alower surface area than the support material, e.g., silicaceous supportmaterial, in one embodiment the support material comprises a silicaceoussupport material that includes at least about 80 wt. %, e.g., at leastabout 85 wt. % or at least about 90 wt. %, high surface area silica inorder to counteract this effect of including a support modifier.

In another aspect, the catalyst composition may be represented by theformula:Pt_(v)Pd_(w)Re_(x)Sn_(y)Ca_(p)Si_(q)O_(r),wherein: (i) the ratio of v:y is between 3:2 and 2:3; and/or (ii) theratio of w:x is between 1:3 and 1:5. Thus, in this embodiment, thecatalyst may comprise (i) platinum and tin; (ii) palladium and rhenium;or (iii) platinum, tin, palladium and rhenium. p and q preferably areselected such that p:q is from 1:20 to 1:200 with r being selected tosatisfy valence requirements and v and w being selected such that:

$0.005 \leq \frac{\left( {{3.25\; v} + {1.75\; w}} \right)}{q} \leq 0.05$

In this aspect, the process conditions and values of v, w, x, y, p, q,and r are preferably chosen such that at least 70% of the acetic acid,e.g., at least 80% or at least 90%, that is converted is converted to acompound selected from the group consisting of ethanol and ethyl acetatewhile less than 4% of the acetic acid is converted to alkanes. Morepreferably, the process conditions and values of v, w, x, y, p, q, and rare preferably chosen such that at least 70% of the acetic acid, e.g.,at least 80% or at least 90%, that is converted is converted to ethanol,while less than 4% of the acetic acid is converted to alkanes. In manyembodiments of the present invention, p is selected, in view of anyminor impurities present, to ensure that the surface of the support isessentially free of active Brønsted acid sites.

In another aspect, the composition of the catalyst comprises:Pt_(v)Pd_(w)Re_(x)Sn_(y)Al_(z)Ca_(p)Si_(q)O_(r),wherein: (i) v and y are between 3:2 and 2:3; and/or (ii) w and x arebetween 1:3 and 1:5. p and z and the relative locations of aluminum andcalcium atoms present preferably are controlled such that Brønsted acidsites present upon the surface thereof are balanced by the supportmodifier, e.g., calcium metasilicate; p and q are selected such that p:qis from 1:20 to 1:200 with r being selected to satisfy valencerequirements and v and w are selected such that:

$0.005 \leq \frac{\left( {{3.25\; v} + {1.75\; w}} \right)}{q} \leq 0.05$

Preferably, in this aspect, the catalyst has a surface area of at leastabout 100 m²/g, e.g., at least about 150 m²/g, at least about 200 m²/gor most preferably at least about 250 m²/g, and z and p≧z. In manyembodiments of the present invention, p is selected, in view of anyminor impurities present, to also ensure that the surface of the supportis substantially free of active Brønsted acid sites which seem tofacilitate conversion of ethanol into ethyl acetate. Thus, as with theprevious embodiment, the process conditions and values of v, w, x, y, p,q, and r preferably are chosen such that at least 70% of the aceticacid, e.g., at least 80% or at least 90%, that is converted is convertedto ethanol, while less than 4% of the acetic acid is converted toalkanes.

Accordingly, without being bound by theory, modification andstabilization of oxidic support materials for the catalysts of thepresent invention by incorporation of non-volatile support modifiershaving either the effect of: counteracting acid sites present upon thesupport surface or the effect of thermally stabilizing the surface makesit possible to achieve desirable improvements in selectivity to ethanol,prolonged catalyst life, or both. In general, support modifiers based onoxides in their most stable valence state will have low vapor pressuresand thus have low volatility or are rather non-volatile. Accordingly, itis preferred that the support modifiers are provided in amountssufficient to: (i) counteract acidic sites present on the surface of thesupport material; (ii) impart resistance to shape change underhydrogenation temperatures; or (iii) both. Without being bound bytheory, imparting resistance to shape change refers to impartingresistance, for example, to sintering, grain growth, grain boundarymigration, migration of defects and dislocations, plastic deformationand/or other temperature induced changes in microstructure.

Catalysts of the present invention are particulate catalysts in thesense that, rather than being impregnated in a wash coat onto amonolithic carrier similar to automotive catalysts and diesel soot trapdevices, the catalysts of the invention preferably are formed intoparticles, sometimes also referred to as beads or pellets, having any ofa variety of shapes and the catalytic metals are provided to thereaction zone by placing a large number of these shaped catalysts in thereactor. Commonly encountered shapes include extrudates of arbitrarycross-section taking the form of a generalized cylinder in the sensethat the generators defining the surface of the extrudate are parallellines. As indicated above, any convenient particle shape includingpellets, extrudates, spheres, spray dried microspheres, rings,pentarings, trilobes, quadrilobes and multi-lobal shapes may be used,although cylindrical pellets are preferred. Typically, the shapes arechosen empirically based upon perceived ability to contact the vaporphase with the catalytic agents effectively.

One advantage of catalysts of the present invention is the stability oractivity of the catalyst for producing ethanol. Accordingly, it can beappreciated that the catalysts of the present invention are fullycapable of being used in commercial scale industrial applications forhydrogenation of acetic acid, particularly in the production of ethanol.In particular, it is possible to achieve such a degree of stability suchthat catalyst activity will have rate of productivity decline that isless than 6% per 100 hours of catalyst usage, e.g., less than 3% per 100hours or less than 1.5% per 100 hours. Preferably, the rate ofproductivity decline is determined once the catalyst has achievedsteady-state conditions.

In one embodiment, when the catalyst support comprises high puritysilica, with calcium metasilicate as a support modifier, the catalystactivity may extend or stabilize, the productivity and selectivity ofthe catalyst for prolonged periods extending into over one week, overtwo weeks, and even months, of commercially viable operation in thepresence of acetic acid vapor at temperatures of 125° C. to 350° C. atspace velocities of greater than 2500 hr⁻¹.

The catalyst compositions of the invention preferably are formed throughmetal impregnation of the modified support, although other processessuch as chemical vapor deposition may also be employed. Before themetals are impregnated, it typically is desired to form the modifiedsupport, for example, through a step of impregnating the supportmaterial with the support modifier. A precursor to the support modifier,such as an acetate or a nitrate, may be used. In one aspect, the supportmodifier, e.g., CaSiO₃, is added to the support material, e.g., SiO₂.For example, an aqueous suspension of the support modifier may be formedby adding the solid support modifier to deionized water, followed by theaddition of colloidal support material thereto. The resulting mixturemay be stirred and added to additional support material using, forexample, incipient wetness techniques in which the support modifier isadded to a support material having the same pore volume as the volume ofthe support modifier solution. Capillary action then draws the supportmodifier into the pores in the support material. The modified supportcan then be formed by drying and calcining to drive off water and anyvolatile components within the support modifier solution and depositingthe support modifier on the support material. Drying may occur, forexample, at a temperature of from 50° C. to 300° C., e.g., from 100° C.to 200° C. or about 120° C., optionally for a period of from 1 to 24hours, e.g., from 3 to 15 hours or from 6 to 12 hours. Once formed, themodified supports may be shaped into particles having the desired sizedistribution, e.g., to form particles having an average particle size inthe range of from 0.2 to 0.4 cm. The supports may be extruded,pelletized, tabletized, pressed, crushed or sieved to the desired sizedistribution. Any of the known methods to shape the support materialsinto desired size distribution can be employed. Calcining of the shapedmodified support may occur, for example, at a temperature of from 250°C. to 800° C., e.g., from 300 to 700° C. or about 500° C., optionallyfor a period of from 1 to 12 hours, e.g., from 2 to 10 hours, from 4 to8 hours or about 6 hours.

In a preferred method of preparing the catalyst, the metals areimpregnated onto the modified support. A precursor of the first metal(first metal precursor) preferably is used in the metal impregnationstep, such as a water soluble compound or water dispersiblecompound/complex that includes the first metal of interest. Depending onthe metal precursor employed, the use of a solvent, such as water,glacial acetic acid or an organic solvent, may be preferred. The secondmetal also preferably is impregnated into the modified support from asecond metal precursor. If desired, a third metal or third metalprecursor may also be impregnated into the modified support.

Impregnation occurs by adding, optionally drop wise, either or both thefirst metal precursor and/or the second metal precursor and/oradditional metal precursors, preferably in suspension or solution, tothe dry modified support. The resulting mixture may then be heated,e.g., optionally under vacuum, in order to remove the solvent.Additional drying and calcining may then be performed, optionally withramped heating to form the final catalyst composition. Upon heatingand/or the application of vacuum, the metal(s) of the metal precursor(s)preferably decompose into their elemental (or oxide) form. In somecases, the completion of removal of the liquid carrier, e.g., water, maynot take place until the catalyst is placed into use and calcined, e.g.,subjected to the high temperatures encountered during operation. Duringthe calcination step, or at least during the initial phase of use of thecatalyst, such compounds are converted into a catalytically active formof the metal or a catalytically active oxide thereof.

Impregnation of the first and second metals (and optional additionalmetals) into the modified support may occur simultaneously(co-impregnation) or sequentially. In simultaneous impregnation, thefirst and second metal precursors (and optionally additional metalprecursors) are mixed together and added to the modified supporttogether, followed by drying and calcination to form the final catalystcomposition. With simultaneous impregnation, it may be desired to employa dispersion agent, surfactant, or solubilizing agent, e.g., ammoniumoxalate, to facilitate the dispersing or solubilizing of the first andsecond metal precursors in the event the two precursors are incompatiblewith the desired solvent, e.g., water.

In sequential impregnation, the first metal precursor is first added tothe modified support followed by drying and calcining, and the resultingmaterial is then impregnated with the second metal precursor followed byan additional drying and calcining step to form the final catalystcomposition. Additional metal precursors (e.g., a third metal precursor)may be added either with the first and/or second metal precursor or an aseparate third impregnation step, followed by drying and calcination. Ofcourse, combinations of sequential and simultaneous impregnation may beemployed if desired.

Suitable metal precursors include, for example, metal halides, aminesolubilized metal hydroxides, metal nitrates or metal oxalates. Forexample, suitable compounds for platinum precursors and palladiumprecursors include chloroplatinic acid, ammonium chloroplatinate, aminesolubilized platinum hydroxide, platinum nitrate, platinum tetraammonium nitrate, platinum chloride, platinum oxalate, palladiumnitrate, palladium tetra ammonium nitrate, palladium chloride, palladiumoxalate, sodium palladium chloride, and sodium platinum chloride.Generally, both from the point of view of economics and environmentalaspects, aqueous solutions of soluble compounds of platinum arepreferred. In one embodiment, the first metal precursor is not a metalhalide and is substantially free of metal halides. Without being boundto theory, such non-(metal halide) precursors are believed to increaseselectivity to ethanol. A particularly preferred precursor to platinumis platinum ammonium nitrate, Pt(NH₃)₄(NO₄)₂.

In one aspect, the “promoter” metal or metal precursor is first added tothe modified support, followed by the “main” or “primary” metal or metalprecursor. Of course the reverse order of addition is also possible.Exemplary precursors for promoter metals include metal halides, aminesolubilized metal hydroxides, metal nitrates or metal oxalates. Asindicated above, in the sequential embodiment, each impregnation steppreferably is followed by drying and calcination. In the case ofpromoted bimetallic catalysts as described above, a sequentialimpregnation may be used, starting with the addition of the promotermetal followed by a second impregnation step involving co-impregnationof the two principal metals, e.g., Pt and Sn.

As an example, PtSn/CaSiO₃ on SiO₂ may be prepared by a firstimpregnation of CaSiO₃ onto the SiO₂, followed by the co-impregnationwith Pt(NH₃)₄(NO₄)₂ and Sn(AcO)₂. Again, each impregnation step may befollowed by drying and calcination steps. In most cases, theimpregnation may be carried out using metal nitrate solutions. However,various other soluble salts, which upon calcination release metal ions,can also be used. Examples of other suitable metal salts forimpregnation include, metal acids, such as perrhenic acid solution,metal oxalates, and the like. In those cases where substantially pureethanol is to be produced, it is generally preferable to avoid the useof halogenated precursors for the platinum group metals, using thenitrogenous amine and/or nitrate based precursors instead.

The process of hydrogenating acetic acid to form ethanol according toone embodiment of the invention may be conducted in a variety ofconfigurations using a fixed bed reactor or a fluidized bed reactor asone of skill in the art will readily appreciate. In many embodiments ofthe present invention, an “adiabatic” reactor can be used; that is,there is little or no need for internal plumbing through the reactionzone to add or remove heat. Alternatively, a shell and tube reactorprovided with a heat transfer medium can be used. In many cases, thereaction zone may be housed in a single vessel or in a series of vesselswith heat exchangers therebetween. It is considered significant thatacetic acid reduction processes using the catalysts of the presentinvention may be carried out in adiabatic reactors as this reactorconfiguration is typically far less capital intensive than tube andshell configurations.

Typically, the catalyst is employed in a fixed bed reactor, e.g., in theshape of an elongated pipe or tube where the reactants, typically in thevapor form, are passed over or through the catalyst. Other reactors,such as fluid or ebullient bed reactors, can be employed, if desired. Insome instances, the hydrogenation catalysts may be used in conjunctionwith an inert material to regulate the pressure drop of the reactantstream through the catalyst bed and the contact time of the reactantcompounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may therange from of 125° C. to 350° C., e.g., from 200° C. to 325° C., from225° C. to about 300° C., or from 250° C. to about 300° C. The pressuremay range from 10 KPa to 3000 KPa (about 0.1 to 30 atmospheres), e.g.,from 50 KPa to 2300 KPa, or from 100 KPa to 1500 KPa. The reactants maybe fed to the reactor at a gas hourly space velocities (GHSV) of greaterthan 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greater than 2500 hr⁻¹ andeven greater than 5000 hr⁻¹. In terms of ranges the GHSV may range from50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500 hr⁻¹.

In another aspect of the process of this invention, the hydrogenation iscarried out at a pressure just sufficient to overcome the pressure dropacross the catalytic bed at the GHSV selected, although there is no barto the use of higher pressures, it being understood that considerablepressure drop through the reactor bed may be experienced at high spacevelocities, e.g., 5000 hr⁻¹ or 6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than4:1, e.g., greater than 5:1 or greater than 10:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 30seconds.

The acetic acid may be vaporized at the reaction temperature, and thenthe vaporized acetic acid can be fed along with hydrogen in undilutedstate or diluted with a relatively inert carrier gas, such as nitrogen,argon, helium, carbon dioxide and the like. For reactions run in thevapor phase, the temperature should be controlled in the system suchthat it does not fall below the dew point of acetic acid.

In particular, using catalysts and processes of the present inventionmay achieve favorable conversion of acetic acid and favorableselectivity and productivity to ethanol. For purposes of the presentinvention, the term conversion refers to the amount of acetic acid inthe feed that is convert to a compound other than acetic acid.Conversion is expressed as a mole percentage based on acetic acid in thefeed.

The conversion of acetic acid (AcOH) is calculated from gaschromatography (GC) data using the following equation:

${{AcOH}\mspace{14mu}{{Conv}.\mspace{14mu}(\%)}} = {100*\frac{\begin{matrix}{{{mmol}{\mspace{11mu}\;}{AcOH}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)} -} \\{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}\left( {G\; C} \right)}\end{matrix}}{{mmol}{\mspace{11mu}\;}{AcOH}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)}}$

For purposes of the present invention, the conversion may be at least10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%, atleast 70% or at least 80%. Although catalysts that have high conversionsare desirable, such as at least 80% or at least 90%, a low conversionmay be acceptable at high selectivity for ethanol. It is, of course,well understood that in many cases, it is possible to compensate forconversion by appropriate recycle streams or use of larger reactors, butit is more difficult to compensate for poor selectivity.

“Selectivity” is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 50 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 50%.Selectivity to ethanol (EtOH) is calculated from gas chromatography (GC)data using the following equation:

${{EtOH}\mspace{14mu}{{Sel}.\mspace{14mu}(\%)}} = {100*\frac{{mmol}\mspace{14mu}{EtOH}\mspace{14mu}\left( {G\; C} \right)}{\begin{matrix}{\frac{{Total}\mspace{14mu}{mmol}\mspace{14mu}{C\left( {G\; C} \right)}}{2} -} \\{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)}\end{matrix}}}$

wherein “Total mmol C (GC)” refers to total mmols of carbon from all ofthe products analyzed by gas chromatograph.

For purposes of the present invention, the selectivity to ethoxylates ofthe catalyst is at least 60%, e.g., at least 70%, or at least 80%. Asused herein, the term “ethoxylates” refers specifically to the compoundsethanol, acetaldehyde, and ethyl acetate. Preferably, the selectivity toethanol is at least 80%, e.g., at least 85% or at least 88%. Inembodiments of the present invention is also desirable to have lowselectivity to undesirable products, such as methane, ethane, and carbondioxide. The selectivity to these undesirable products is less than 4%,e.g., less than 2% or less than 1%. Preferably, no detectable amounts ofthese undesirable products are formed during hydrogenation. In severalembodiments of the present invention, formation of alkanes is low,usually under 2%, often under 1%, and in many cases under 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

Productivity refers to the grams of a specified product, e.g., ethanol,formed during the hydrogenation based on the kilogram of catalyst usedper hour. In one embodiment of the present invention, a productivity ofat least 200 grams of ethanol per kilogram catalyst per hour, e.g., atleast 400 grams of ethanol or least 600 grams of ethanol, is preferred.In terms of ranges, the productivity preferably is from 200 to 3,000grams of ethanol per kilogram catalyst per hour, e.g., from 400 to 2,500or from 600 to 2,000.

Some catalysts of the present invention may achieve a conversion ofacetic acid of at least 10%, a selectivity to ethanol of at least 80%,and a productivity of at least 200 g of ethanol per kg of catalyst perhour. A subset of catalysts of the invention may achieve a conversion ofacetic acid of at least 50%, a selectivity to ethanol of at least 80%, aselectivity to undesirable compounds of less than 4%, and a productivityof at least 600 g of ethanol per kg of catalyst per hour.

In another embodiment, the invention is to a crude ethanol productformed by processes of the present invention. The crude ethanol productproduced by the hydrogenation process of the present invention, beforeany subsequent processing, such as purification and separation,typically will comprise primarily unreacted acetic acid and ethanol. Insome exemplary embodiments, the crude ethanol product comprises ethanolin an amount from 15 wt. % to 70 wt. %, e.g., from 20 wt. % to 50 wt. %,or from 25 wt % to 50 wt. %, based on the total weight of the crudeethanol product. Preferably, the crude ethanol product contains at least22 wt. % ethanol, at least 28 wt. % ethanol or at least 44 wt. %ethanol. The crude ethanol product typically will further compriseunreacted acetic acid, depending on conversion, for example, in anamount from 0 to 80 wt %, e.g., from 5 to 80 wt %, from 20 to 70 wt. %,from 28 to 70 wt. % or from 44 to 65 wt. %. Since water is formed in thereaction process, water will also be present in the crude ethanolproduct, for example, in amounts ranging from 5 to 30 wt. %, e.g., from10 to 30 wt. % or from 10 to 26 wt. %. Other components, such as, forexample, esters, ethers, aldehydes, ketones, alkanes, and carbondioxide, if detectable, collectively may be present in amounts less than10 wt. %, e.g., less than 6 or less than 4 wt. %. In terms of rangesother components may be present in an amount from 0.1 to 10 wt. %, e.g.,from 0.1 to 6 wt. %, or from 0.1 to 4 wt. %. Thus, exemplary crudeethanol compositional ranges in various embodiments of the invention areprovided below in Table 2.

TABLE 2 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 15-70  15-70 20-5025-50 Acetic Acid 5-80 20-70 28-70 44-65 Water 5-30  5-30 10-30 10-26Other <10 <10 <6 <4

In a preferred embodiment, the crude ethanol product is formed over aplatinum/tin catalyst on a modified silica support, e.g., modified withCaSiO₃. Depending on the specific catalyst and process conditionsemployed, the crude ethanol product may have any of the compositionsindicated below in Table 3.

TABLE 3 CRUDE ETHANOL PRODUCT COMPOSITIONS Comp. A Comp. B Comp. CComponent Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Ethanol 17 26 45Acetic Acid 74 53 20 Water 7 13 25 Other 2 8 10

The raw materials used in connection with the process of this inventionmay be derived from any suitable source including natural gas,petroleum, coal, biomass and so forth. It is well known to produceacetic acid through methanol carbonylation, acetaldehyde oxidation,ethylene oxidation, oxidative fermentation, and anaerobic fermentation.As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive compared to natural gas, it may become advantageous to produceacetic acid from synthesis gas (“syn gas”) that is derived from anyavailable carbon source. U.S. Pat. No. 6,232,352 to Vidalin, thedisclosure of which is incorporated herein by reference, for example,teaches a method of retrofitting a methanol plant for the manufacture ofacetic acid. By retrofitting a methanol plant, the large capital costsassociated with CO generation for a new acetic acid plant aresignificantly reduced or largely eliminated. All or part of the syn gasis diverted from the methanol synthesis loop and supplied to a separatorunit to recover CO and hydrogen, which are then used to produce aceticacid. In addition to acetic acid, the process can also be used to makehydrogen which may be utilized in connection with this invention.

U.S. Pat. No. RE 35,377 to Steinberg et al., also incorporated herein byreference, provides a method for the production of methanol byconversion of carbonaceous materials such as oil, coal, natural gas andbiomass materials. The process includes hydrogasification of solidand/or liquid carbonaceous materials to obtain a process gas which issteam pyrolized with additional natural gas to form synthesis gas. Thesyn gas is converted to methanol which may be carbonylated to aceticacid. The method likewise produces hydrogen which may be used inconnection with this invention as noted above. See also, U.S. Pat. No.5,821,111 to Grady et al., which discloses a process for convertingwaste biomass through gasification into synthesis gas as well as U.S.Pat. No. 6,685,754 to Kindig et al., the disclosures of which areincorporated herein by reference.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078 to Scates et al., theentirety of which is incorporated herein by reference. The crude vaporproduct, for example, may be fed directly to the ethanol synthesisreaction zones of the present invention without the need for condensingthe acetic acid and light ends or removing water, saving overallprocessing costs.

Ethanol, obtained from hydrogenation processes of the present invention,may be used in its own right as a fuel or subsequently converted toethylene which is an important commodity feedstock as it can beconverted to polyethylene, vinyl acetate and/or ethyl acetate or any ofa wide variety of other chemical products. For example, ethylene canalso be converted to numerous polymer and monomer products. Thedehydration of ethanol to ethylene is shown below.

Any of known dehydration catalysts can be employed in to dehydrateethanol, such as those described in copending applications U.S.application Ser. Nos. 12/221,137 and 12/221,138, the entire contents anddisclosures of which are hereby incorporated by reference. A zeolitecatalyst, for example, may be employed as the dehydration catalyst.While any zeolite having a pore diameter of at least about 0.6 nm can beused, preferred zeolites include dehydration catalysts selected from thegroup consisting of mordenites, ZSM-5, a zeolite X and a zeolite Y.Zeolite X is described, for example, in U.S. Pat. No. 2,882,244 andzeolite Y in U.S. Pat. No. 3,130,007, the entireties of which are herebyincorporated by reference.

Ethanol may also be used as a fuel, in pharmaceutical products,cleansers, sanitizers, hydrogenation transport or consumption. Ethanolmay also be used as a source material for making ethyl acetate,aldehydes, and higher alcohols, especially butanol. In addition, anyester, such as ethyl acetate, formed during the process of makingethanol according to the present invention may be further reacted withan acid catalyst to form additional ethanol as well as acetic acid,which may be recycled to the hydrogenation process.

The invention is described in detail below with reference to numerousembodiments for purposes of exemplification and illustration only.Modifications to particular embodiments within the spirit and scope ofthe present invention, set forth in the appended claims, will be readilyapparent to those of skill in the art.

The following examples describe the procedures used for the preparationof various catalysts employed in the process of this invention.

EXAMPLES

Catalyst Preparations (General)

The catalyst supports were dried at 120° C. overnight under circulatingair prior to use. All commercial supports (i.e., SiO₂, ZrO₂) were usedas a 14/30 mesh, or in its original shape ( 1/16 inch or ⅛ inch pellets)unless mentioned otherwise. Powdered materials (i.e., CaSiO₃) werepelletized, crushed and sieved after the metals had been added. Theindividual catalyst preparations are described in detail below.

Example 1 SiO₂—CaSiO₃(5)-Pt(3)-Sn(1.8) Catalyst

The catalyst was prepared by first adding CaSiO₃ (Aldrich) to the SiO₂catalyst support, followed by the addition of Pt/Sn. First, an aqueoussuspension of CaSiO₃ (≦200 mesh) was prepared by adding 0.52 g of thesolid to 13 ml of deionized H₂O, followed by the addition of 1.0 ml ofcolloidal SiO₂ (15 wt. % solution, NALCO). The suspension was stirredfor 2 hours at room temperature and then added to 10.0 g of SiO₂catalyst support (14/30 mesh) using incipient wetness technique. Afterstanding for 2 hours, the material was evaporated to dryness, followedby drying at 120° C. overnight under circulating air and calcination at500° C. for 6 hours. All of the SiO₂—CaSiO₃ material was then used forPt/Sn metal impregnation.

The catalysts were prepared by first adding Sn(OAc)₂ (tin acetate,Sn(OAc)₂ from Aldrich) (0.4104 g, 1.73 mmol) to a vial containing 6.75ml of 1:1 diluted glacial acetic acid (Fisher). The mixture was stirredfor 15 min at room temperature, and then, 0.6711 g (1.73 mmol) of solidPt(NH₃)₄(NO₃)₂ (Aldrich) were added. The mixture was stirred for another15 min at room temperature, and then added drop wise to 5.0 g ofSiO₂—CaSiO₃ support, in a 100 ml round-bottomed flask. The metalsolution was stirred continuously until all of the Pt/Sn mixture hadbeen added to the SiO₂—CaSiO₃ support while rotating the flask afterevery addition of metal solution. After completing the addition of themetal solution, the flask containing the impregnated catalyst was leftstanding at room temperature for two hours. The flask was then attachedto a rotor evaporator (bath temperature 80° C.), and evacuated untildried while slowly rotating the flask. The material was then driedfurther overnight at 120° C., and then calcined using the followingtemperature program: 25→160° C./ramp 5.0 deg/min; hold for 2.0 hours;160→500° C./ramp 2.0 deg/min; hold for 4 hours. Yield: 11.21 g of darkgrey material.

Example 2 KA160-CaSiO₃(8)-Pt(3)-Sn(1.8)

The material was prepared by first adding CaSiO₃ to the KA160 catalystsupport (SiO₂-(0.05) Al₂O₃, Sud Chemie, 14/30 mesh), followed by theaddition of Pt/Sn. First, an aqueous suspension of CaSiO₃ (≦200 mesh)was prepared by adding 0.42 g of the solid to 3.85 ml of deionized H₂O,followed by the addition of 0.8 ml of colloidal SiO₂ (15 wt. % solution,NALCO). The suspension was stirred for 2 hours at room temperature andthen added to 5.0 g of KA160 catalyst support (14/30 mesh) usingincipient wetness technique. After standing for 2 hours, the materialwas evaporated to dryness, followed by drying at 120° C. overnight undercirculating air and calcinations at 500° C. for 6 hours. All of theKA160-CaSiO₃ material was then used for Pt/Sn metal impregnation.

The catalysts were prepared by first adding Sn(OAc)₂ (tin acetate,Sn(OAc)₂ from Aldrich) (0.2040 g, 0.86 mmol) to a vial containing 6.75ml of 1:1 diluted glacial acetic acid (Fisher). The mixture was stirredfor 15 min at room temperature, and then, 0.3350 g (0.86 mmol) of solidPt(NH₃)₄(NO₃)₂ (Aldrich) were added. The mixture was stirred for another15 min at room temperature, and then added drop wise to 5.0 g ofSiO₂—CaSiO₃ support, in a 100 ml round-bottomed flask. After completingthe addition of the metal solution, the flask containing the impregnatedcatalyst was left standing at room temperature for two hours. The flaskwas then attached to a rotor evaporator (bath temperature 80° C.), andevacuated until dried while slowly rotating the flask. The material wasthen dried further overnight at 120° C., and then calcined using thefollowing temperature program: 25→160° C./ramp 5.0 deg/min; hold for 2.0hours; 160→500° C./ramp 2.0 deg/min; hold for 4 hours. Yield: 5.19 g oftan-colored material.

Example 3 SiO₂—CaSiO₃(2.5)-Pt(1.5)-Sn(0.9)

This catalyst was prepared in the same manner as Example 1, with thefollowing starting materials: 0.26 g of CaSiO₃ as a support modifier;0.5 ml of colloidal SiO₂ (15 wt. % solution, NALCO), 0.3355 g (0.86mmol) of Pt(NH₃)₄(NO₃)₂; and 0.2052 g (0.86 mmol) of Sn(OAc)₂. Yield:10.90 g of dark grey material.

Example 4 SiO₂+MgSiO₃—Pt(1.0)-Sn(1.0)

This catalyst was prepared in the same manner as Example 1, with thefollowing starting materials: 0.69 g of Mg(AcO) as a support modifier;1.3 g of colloidal SiO₂ (15 wt. % solution, NALCO), 0.2680 g (0.86 mmol)of Pt(NH₃)₄(NO₃)₂; and 0.1640 g (0.86 mmol) of Sn(OAc)₂. Yield: 8.35 g.The SiO₂ support was impregnated with a solution of Mg(AcO) andcolloidal SiO₂. The support was dried and then calcined to 700° C.

Example 5 SiO₂—CaSiO₃(5)-Re(4.5)-Pd(1)

The SiO₂—CaSiO₃(5) modified catalyst support was prepared as describedin Example 1. The Re/Pd catalyst was prepared then by impregnating theSiO₂—CaSiO₃(5) ( 1/16 inch extrudates) with an aqueous solutioncontaining NH₄ReO₄ and Pd(NO₃)₂. The metal solutions were prepared byfirst adding NH₄ReO₄ (0.7237 g, 2.70 mmol) to a vial containing 12.0 mlof deionized H₂O. The mixture was stirred for 15 min at roomtemperature, and 0.1756 g (0.76 mmol) of solid Pd(NO₃)₂ was then added.The mixture was stirred for another 15 min at room temperature, and thenadded drop wise to 10.0 g of dry SiO₂-(0.05)CaSiO₃ catalyst support in a100 ml round-bottomed flask. After completing the addition of the metalsolution, the flask containing the impregnated catalyst was leftstanding at room temperature for two hours. All other manipulations(drying, calcination) were carried out as described in Example 1. Yield:10.9 g of brown material.

Example 6 SiO₂—ZnO(5)-Pt(1)-Sn(1)

Powdered and meshed high surface area silica NPSG SS61138 (100 g) ofuniform particle size distribution of about 0.2 mm was dried at 120° C.in a circulating air oven atmosphere overnight and then cooled to roomtemperature. To this was added a solution of zinc nitrate hexahydrate.The resulting slurry was dried in an oven gradually heated to 110° C.(>2 hours, 10° C./min.) then calcined. To this was added a solution ofplatinum nitrate (Chempur) in distilled water and a solution of tinoxalate (Alfa Aesar) (1.74 g) in dilute nitric acid (1N, 8.5 ml) Theresulting slurry was dried in an oven gradually heated to 110° C. (>2hours, 10° C./min.). The impregnated catalyst mixture was then calcinedat 500° C. (6 hours, 1° C./min).

In addition, the following comparative catalysts were also prepared.

Example 7 Comparative

TiO₂—CaSiO₃(5)-Pt(3)-Sn(1.8). The material was prepared by first addingCaSiO₃ to the TiO₂ catalyst (Anatase, 14/30 mesh) support, followed bythe addition of Pt/Sn as described in Example 1. First, an aqueoussuspension of CaSiO₃ (≦200 mesh) was prepared by adding 0.52 g of thesolid to 7.0 ml of deionized H₂O, followed by the addition of 1.0 ml ofcolloidal SiO₂ (15 wt. % solution, NALCO). The suspension was stirredfor 2 h at room temperature and then added to 10.0 g of TiO₂ catalystsupport (14/30 mesh) using incipient wetness technique. After standingfor 2 hours, the material was evaporated to dryness, followed by dryingat 120° C. overnight under circulating air and calcination at 500° C.for 6 hours. All of the TiO₂—CaSiO₃ material was then used for Pt/Snmetal impregnation using 0.6711 g (1.73 mmol) of Pt(NH₃)₄(NO₃)₂ and0.4104 g (1.73 mmol) of Sn(OAc)₂ following the procedure described inExample 1. Yield: 11.5 g of light grey material.

Example 8 Comparative

Sn(0.5) on High Purity Low Surface Area Silica. Powdered and meshed highpurity low surface area silica (100 g) of uniform particle sizedistribution of about 0.2 mm was dried at 120° C. in an oven undernitrogen atmosphere overnight and then cooled to room temperature. Tothis was added a solution of tin oxalate (Alfa Aesar) (1.74 g) in dilutenitric acid (1 N, 8.5 ml). The resulting slurry was dried in an ovengradually heated to 110° C. (>2 hours, 10° C./min.). The impregnatedcatalyst mixture was then calcined at 500° C. (6 hours, 1° C./min).

Example 9 Comparative

Pt(2)-Sn(2) on High Surface Area Silica. Powdered and meshed highsurface area silica NPSG SS61138 (100 g) of uniform particle sizedistribution of about 0.2 mm was dried at 120° C. in a circulating airoven atmosphere overnight and then cooled to room temperature. To thiswas added a solution of nitrate hexahydrate (Chempur). The resultingslurry was dried in an oven gradually heated to 110° C. (>2 hours, 10°C./min.) then calcined. To this was added a solution of platinum nitrate(Chempur) in distilled water and a solution of tin oxalate (Alfa Aesar)in dilute nitric acid. The resulting slurry was dried in an ovengradually heated to 110° C. (>2 hours, 10° C./min.). The impregnatedcatalyst mixture was then calcined at 500° C. (6 hours, 1° C./min).

Example 10 Comparative

KA160-Pt(3)-Sn(1.8). The material was prepared by incipient wetnessimpregnation of KA160 catalyst support (SiO₂-(0.05) Al₂O₃, Sud Chemie,14/30 mesh) as described in Example 16. The metal solutions wereprepared by first adding Sn(OAc)₂ (0.2040 g, 0.86 mmol) to a vialcontaining 4.75 ml of 1:1 diluted glacial acetic acid. The mixture wasstirred for 15 min at room temperature, and then, 0.3350 g (0.86 mmol)of solid Pt(NH₃)₄(NO₃)₂ were added. The mixture was stirred for another15 min at room temperature, and then added drop wise to 5.0 g of dryKA160 catalyst support (14/30 mesh) in a 100 ml round-bottomed flask.All other manipulations, drying and calcination was carried out asdescribed in Example 16. Yield: 5.23 g of tan-colored material.

Example 11 Comparative

SiO₂—SnO₂(5)-Pt(1)-Zn(1). Powdered and meshed high surface area silicaNPSG SS61138 (100 g) of uniform particle size distribution of about 0.2mm was dried at 120° C. in a circulating air oven atmosphere overnightand then cooled to room temperature. To this was added a solution of tinacetate (Sn(OAc)₂). The resulting slurry was dried in an oven graduallyheated to 110° C. (>2 hours, 10° C./min.) then calcined. To this wasadded a solution of platinum nitrate (Chempur) in distilled water and asolution of tin oxalate (Alfa Aesar) in dilute nitric acid The resultingslurry was dried in an oven gradually heated to 110° C. (>2 hours, 10°C./min.). The impregnated catalyst mixture was then calcined at 500° C.(6 hours, 1° C./min).

Example 12 Comparative

SiO₂—TiO₂(10)-Pt(3)-Sn(1.8). The TiO₂-modified silica support wasprepared as follows. A solution of 4.15 g (14.6 mmol) of Ti{OCH(CH₃)₂}₄in 2-propanol (14 ml) was added dropwise to 10.0 g of SiO₂ catalystsupport ( 1/16 inch extrudates) in a 100 ml round-bottomed flask. Theflask was left standing for two hours at room temperature, and thenevacuated to dryness using a rotor evaporator (bath temperature 80° C.).Next, 20 ml of deionized H₂O was slowly added to the flask, and thematerial was left standing for 15 min. The resulting water/2-propanolwas then removed by filtration, and the addition of H₂O was repeated twomore times. The final material was dried at 120° C. overnight undercirculation air, followed by calcination at 500° C. for 6 hours. All ofthe SiO₂—TiO₂ material was then used for Pt/Sn metal impregnation using0.6711 g (1.73 mmol) of Pt(NH₃)₄(NO₃)₂ and 0.4104 g (1.73 mmol) ofSn(OAc)₂ following the procedure described above for Example 1. Yield:11.98 g of dark grey 1/16 inch extrudates.

Example 13 Comparative

SiO₂—WO₃(10)-Pt(3)-Sn(1.8). The WO₃-modified silica support was preparedas follows. A solution of 1.24 g (0.42 mmol) of (NH₄)₆H₂W₁₂O₄₀.n H₂O,(AMT) in deionized H₂O (14 ml) was added dropwise to 10.0 g of SiO₂NPSGSS 61138 catalyst support (SA=250 m²/g, 1/16 inch extrudates) in a100 ml round-bottomed flask. The flask was left standing for two hoursat room temperature, and then evacuated to dryness using a rotorevaporator (bath temperature 80° C.). The resulting material was driedat 120° C. overnight under circulation air, followed by calcination at500° C. for 6 hours. All of the (light yellow) SiO₂—WO₃ material wasthen used for Pt/Sn metal impregnation using 0.6711 g (1.73 mmol) ofPt(NH₃)₄(NO₃)₂ and 0.4104 g (1.73 mmol) of Sn(OAc)₂ following theprocedure described above for Example 1. Yield: 12.10 g of dark grey1/16 inch extrudates.

Example 14 Hydrogenation of Acetic Acid Over Catalysts from Examples1-13 and Gas Chromatographic (GC) Analysis of the Crude Ethanol Product

Catalyst of Examples 1-13 were tested to determine the selectivity andproductivity to ethanol as shown in Table 4.

The reaction feed liquid of acetic acid was evaporated and charged tothe reactor along with hydrogen and helium as a carrier gas with anaverage combined gas hourly space velocity (GHSV), temperature, andpressure as indicated in Table 4. The feed stream contained a mole ratiohydrogen to acetic acid as indicated in Table 4.

The analysis of the products (crude ethanol composition) was carried outby online GC. A three channel compact GC equipped with one flameionization detector (FID) and 2 thermal conducting detectors (TCDs) wasused to analyze the reactants and products. The front channel wasequipped with an FID and a CP-Sil 5 (20 m)+WaxFFap (5 m) column and wasused to quantify: Acetaldehyde; Ethanol; Acetone; Methyl acetate; Vinylacetate; Ethyl acetate; Acetic acid; Ethylene glycol diacetate; Ethyleneglycol; Ethylidene diacetate; and Paraldehyde. The middle channel wasequipped with a TCD and Porabond Q column and was used to quantify: CO₂;ethylene; and ethane. The back channel was equipped with a TCD andMolsieve 5A column and was used to quantify: Helium; Hydrogen; Nitrogen;Methane; and Carbon monoxide.

Prior to reactions, the retention times of the different components weredetermined by spiking with individual compounds and the GCs werecalibrated either with a calibration gas of known composition or withliquid solutions of known compositions. This allowed the determinationof the response factors for the various components.

TABLE 4 Reaction Conditions Ratio of Press. Temp. GHSV Conv. ofSelectivity (%) Cat. Ex. Cat. H₂:AcOH (KPa) (° C.) (hr⁻¹) AcOH (%) EtOAcEtOH Inventive 1 SiO₂—CaSiO₃(5)-Pt(3)-Sn(1.8) 5:1 2200 250 2500 24 6 922 KA160-CaSiO₃(8)-Pt(3)-Sn(1.8) 5:1 2200 250 2500 43 13 84 3SiO₂—CaSiO₃(2.5)-Pt(1.5)-Sn(0.9) 10:1  1400 250 2500 26 8 86 4 SiO₂ +MgSiO₃—Pt(1.0)-Sn(1.0) 4:1 1400 250 6570 22 10 88 5SiO₂—CaSiO₃(5)-Re(4.5)-Pd(1) 5:1 1400 250 6570 8 17 83 6SiO₂—ZnO(5)-Pt(1)-Sn(1) 4:1 1400 275 6570 22 21 76 Comparative 7TiO₂—CaSiO₃(5)-Pt(3)-Sn(1.8) 5:1 1400 250 6570 38 78 22 8 Sn(0.5) onSiO₂ 9:1~8:1 2200 250 2500 10 1 9 Pt(2)-Sn(2) on SiO₂ 5:1 1400 296 657034 64 33 9 Pt(2)-Sn(2) on SiO₂ 5:1 1400 280 6570 37 62 36 9 Pt(2)-Sn(2)on SiO₂ 5:1 1400 250 6570 26 63 36 9 Pt(2)-Sn(2) on SiO₂ 5:1 1400 2256570 11 57 42 10 KA160-Pt(3)-Sn(1.8) 5:1 2200 250 2500 61 50 47 11SiO₂—SnO₂(5)-Pt(1)-Zn(1) 4:1 1400 275 6570 13 44 48 12SiO₂—TiO₂(10)-Pt(3)-Sn(1.8) 5:1 1400 250 6570 73 53 47 13SiO₂—WO₃(10)-Pt(3)-Sn(1.8) 5:1 1400 250 6570 17 23 77

Example 15 Catalyst Stability (15 Hours)

Vaporized acetic acid and hydrogen were passed over a hydrogenationcatalyst of the present invention comprising 3 wt. % Pt, 1.5 wt. % Snand 5 wt % CaSiO₃, as a promoter on high purity, high surface areasilica having a surface area of approximately 250 m²/g at a molar ratioof hydrogen to acetic acid of about 5:1 (feed rate of 0.09 g/min HOAc;160 sccm/min H₂; 60 sccm/min N₂) at a temperature of about 225° C.,pressure of 200 psig (about 1400 KPag), and GHSV=6570 hr⁻¹. SiO₂stabilized with 5% CaSiO₃ in hydrogenation of acetic acid was studied ina run of 15 hours duration at 225° C. using a fixed bed continuousreactor system to produce mainly ethanol, acetaldehyde, and ethylacetate through hydrogenation and esterification reactions in a typicalrange of operating conditions employing 2.5 ml solid catalyst (14/30mesh, diluted 1:1 (v/v, with quartz chips, 14/30 mesh). FIG. 3Aillustrates the selectivity, and FIG. 3B illustrates the productivity ofthe catalysts as a function of time on-stream during the initial portionof the catalysts life. From the results of this example as reported inFIG. 3A and FIG. 3B, it can be appreciated that it is possible to attaina selectivity of over 90% and productivity of over 500 g of ethanol perkilogram of catalyst per hour.

Example 16 Catalyst Stability (Over 100 Hours)

Catalyst Stability: SiO₂—CaSiO₃(5)-Pt(3)-Sn(1.8). The catalyticperformance and initial stability of SiO₂—CaSiO₃(5)-Pt(3)-Sn(1.8) wasevaluated at constant temperature (260° C. over 100 hrs of reactiontime. Only small changes in catalyst performance and selectivity wereobserved over the 100 hrs of total reaction time. Acetaldehyde appearedto be the only side product, and its concentration (˜3 wt. %) remainedlargely unchanged over the course of the experiment. A summary ofcatalyst productivity and selectivity is provided in FIGS. 4A and 4B.

Example 17 Catalyst Stability

The procedure of Example 16 was repeated at a temperature of about 250°C. FIGS. 5A and 5B illustrate the productivity and selectivity of thecatalysts as a function of time on-stream during the initial portion ofthe catalysts life. From the results of this example, as reported inFIGS. 5A and 5B, it can be appreciated, that it is still possible toattain a selectivity activity of over 90% but with productivity of over800 g of ethanol per kilogram of catalyst per hour at this temperature.

Example 18

The catalyst of Example 3 was prepared with different loadings ofsupport modifier, CaSiO₃, and produced the following catalysts: (i)SiO₂—Pt(1.5)-Sn(0.9); (ii) SiO₂—CaSiO₃(2.5)-Pt(1.5)-Sn(0.9); (iii)SiO₂—CaSiO₃(5.0)-Pt(1.5)-Sn(0.9); (iv) SiO₂—CaSiO₃(7.5)-Pt(1.5)-Sn(0.9);and (v) SiO₂—CaSiO₃(10)-Pt(1.5)-Sn(0.9). Each catalyst was used inhydrogenating acetic acid at 250° C. and 275° C. under similarconditions, i.e., 1400 bar (200 psig), GHSV of 2500 hr⁻¹ and a 10:1hydrogen to acetic acid molar feed ratio, (683 sccm/min of H₂ to 0.183g/min AcOH). The conversion is shown in FIG. 6A, productivity in FIG.6B, selectivity at 250° C. in FIG. 6C and selectivity at 275° C. in FIG.6D.

As shown in FIG. 6A, the conversion of acetic acid at 250° C. and 275°C. surprisingly increased at CaSiO₃ loadings greater than 2.5 wt. %. Theinitial drop in conversion exhibited from 0 to 2.5 wt. % CaSiO₃ wouldsuggest that conversion would be expected to decrease as more CaSiO₃ isadded. This trend, however, surprisingly reserves as more supportmodifier is added. Increasing conversion also results in increasedproductivity, as shown in FIG. 6B. The selectivities in FIGS. 6C and 6Cshow a slight increase as the amount of support modifier increases.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising: hydrogenatingacetic acid in the presence of a catalyst comprising:Pt_(v)Pd_(w)Re_(x)Sn_(y)Ca_(p)Si_(q)O_(r), wherein: (i) the ratio of v:yis between 3:2 and 2:3, and/or (ii) the ratio of w:x is between 1:3 and1:5; and p and q are selected such that p:q is from 1:20 to 1:200 with rbeing selected to satisfy valence requirements and v and w beingselected such that:$0.005 \leq \frac{\left( {{3.25\; v} + {1.75\; w}} \right)}{q} \leq {0.05.}$2. The process of claim 1, wherein the ratio of v:y is between 3:2 and2:3.
 3. The process of claim 1, wherein the ratio of w:x is between 1:3and 1:5.
 4. A process for producing ethanol, comprising: hydrogenatingacetic acid in the presence of a catalyst comprising:Pt_(v)Pd_(w)Re_(x)Sn_(y)Al_(z)Ca_(p)Si_(q)O_(r), wherein: (i) v and yare between 3:2 and 2:3, and/or (ii) w and x are between 1:3 and 1:5;and p and z and the relative locations of aluminum and calcium atomspresent are controlled such that Brønsted acid sites present upon thesurface thereof are balanced by a support modifier; and p and q areselected such that p:q is from 1:20 to 1:200 with r being selected tosatisfy valence requirements, and v and w are selected such that:$0.005 \leq \frac{\left( {{3.25v} + {1.75w}} \right)}{q} \leq {0.05.}$5. The process of claim 4, wherein the ratio of v:y is between 3:2 and2:3.
 6. The process of claim 4, wherein the ratio of w:x is between 1:3and 1:5.
 7. The process of claim 4, wherein the at least one supportmodifier is selected from the group consisting of (i) alkaline earthmetal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof.